Description
OBJECTIVE
The objective of this assignment is to give you more practice with 2D arrays, representation of data, and basic
strings.
ASSIGNMENT SUBMISSION
To get credit for this assignment, you must
✓ write a program in C that you wrote on your own (no copying or help outside of CSS mentors or TLC or
instructor allowed)
✓ submit your files through Canvas exactly as instructed (naming, compatibility, etc.)
✓ submit your assignment by the due date
PROBLEM STATEMENT
Create a program that reads 24-bit bmp files and generates new versions of the original image. The new versions to
be supported are:
• original converted to sepia tones
• original converted to color pop
• original mirrored along horizontal axis
• original flipped along vertical axis
• your choice of interesting and complex image manipulation
You need to follow the algorithms explained below while processing the images.
BMP files
A 24-bit bmp file is capable of storing 2d images. A file consists of a 54 byte
header and the rest of the file is pixel information. Each pixel is represented
by 3 bytes, where each byte contains the information for blue, green, and
red hues – in this order.
Each hue can be of value 0..255, where 0 signifies
the complete lack of that color, while 255 signifies its full saturation. New
colors are generated by mixing different intensities of this basic color
palette. All together 2563 = 16,777,216 colors can be represented using this
scheme.
Note that the image height and width in pixels correspond to how we store information in a 2D array. In the bmp
format the pixel (0,0) is located at the bottom left (origin of the plane) at locations (0,0), (0,1), (0,2).
Width (x 3)
0 1 2 3 4 5 ….. N
height-1
Pixel 1
B
Pixel 1
G
Pixel 1
R
Pixel 2
B
Pixel 2
G
Pixel 2
R
….. Pixel N
B
Pixel N
G
Pixel N
R
height …
2
1
0
A sample file bmpchange.c is provided to show how to read and write such files, and how blue and green
components of each pixel could be switched. You are to use this file as the basis of your program (for reading and
writing files, just use the provided code).
A few small bmp test files are provided with this homework as well. Since your program will need to ask for the
height and width of the picture in pixels, you may find this information in Ubuntu by right-clicking on the bmp image
file, selecting Properties and then Image tab.
Pixel Manipulation Algorithms
Sepia Algorithm
For each pixel, recalculate its BGR values as:
newBlue = (R * 0.272 + G * 0.534 + B * 0.131)
newGreen = (R * 0.349 + G * 0.686 + B * 0.168)
newRed = (R * 0.393 + G * 0.769 + B * 0.189)
If the new value > 255, make it 255
Color Pop Algorithm
Color pop refers to keeping some pixel colors and making all other grayscale. You will perform color pop based on
the color of the middle pixel of each image (at location width/2 by height/2 – remember that width-wise it really
means three array cells). All pixels whose color are within a certain “distance” to the middle pixel color will remain
the same as in the original image.
All pixels whose color is greater than or equal to the “distance” are changed to
grayscale pixels. To calculate the distance between two pixels, use the formula:
√(red_value_1 – red_value_2)
2 + (green_value_1 – green_value_2)
2 + (blue_value_1 – blue_value_2)
2
To calculate the grayscale of a pixel, use the formula
(blue_value + green_value + red_value) / 3 = average
Replace original BGR values with average, average, average
In our implementation, let’s use the distance of 55 as our threshold for changing between grayscale and color
Vertical Axis Flip
For each row in old image, copy the row in reverse:
Before After
a b c c b a
d e f f e d
g h i i h g
j k l l k j
Horizontal Axis Mirror
For each column in old image:
• Copy the first half as-is
• Copy the second half reversed
Before After
a b c a b c
d e f d e f
g h i d e f
j k l a b c
Before After
a b c a b c
d e f d e f
g h i g h i
j k l d e f
m n o a b c
Your choice of interesting and complex image manipulation
If you would rather replace one of the options above with some other manipulation, feel free to do so. However,
note that to receive credit, the manipulation must include the manipulation of positions and colors. For example,
one interesting idea is to figure out how to “censor” a picture by pixelating it.
PROGRAM SPECIFICATIONS
Your program is to prompt for the name of the input file and its pixel dimensions. Your program has to run exactly as
shown below and follow the same input format. Note that although a file will have a bmp extension, a user will only
enter the part of the name that precedes it, so the program will need to append .bmp; then the user is to be
prompted for height and width (in this order) – assume valid input.
This is a sample run of the program (bold and italics indicate user entries).:
—
Enter the filename: test1
Enter height and width (in pixels): 160 240
Done. Check the generated images.
—
Note that the generated files should be named:
sepia.bmp
pop.bmp
mirror.bmp
flip.bmp
surprise.bmp
Sample input files for processing and sample processed versions of one of them are uploaded into Canvas.
• Your program is to be contained in a single c file named pr2.c
• Your program has to follow basic stylistic features, such as proper indentation (use whitespaces, not tabs),
meaningful variable names, etc.
• Overall, your program is to use at most two 2D variable length arrays: one that contains the original image
and the other that contains the copy of the image
• Open and close files per-need basis
• If you want to copy an entire matrix at once, use memcpy function to do so instead of copying cell by cell, as
in memcpy(matrix2, matrix1, sizeof(matrix1); // this copies matrix 1 into matrix 2
• Your program must compile in gcc gnu 90 – programs that do not compile will receive a grade of 0
• If you use a math library, you will need to compile with -lm flag (note, the first letter is lowercase L as in lion
or letter) at the end, gcc -std=gnu90 pr1.c -lm
• Your program should include the following comments:
o Your name at the top
o Whether you tested your code on the cssgate server or Ubuntu 16.04 LTS Desktop 32-bit
o Comments explaining your logic
o If you choose your own image manipulation, explain it
GRADING
Remember, the programming assignments are graded as pass / no pass only and 85 points (out of 100 are needed to
pass). If you do not pass this assignment, you can turn it in again with assignment 3, 4, or 5.
Each image manipulation implemented according to instructions and running perfectly constitutes 15 points but the
maximum earned here is 60 points (i.e. 4 out of 5 choices)
Proper coding style, meaningful identifiers, etc. is worth 15 points
Program that runs according to the specs that conserves resources is worth 25 points. Conserving resources in this
instance means things such as:
• variables are never declared inside loops
• the program reads once into a 2d array and uses the in-memory image version for processing
• at most two 2d arrays are used
• input and output streams are only open when needed
PROGRAM SUBMISSION
On or before the due date for assignment 2, use the link posted in Canvas next to Programming Assignment 2 to
submit your C code. Make sure you know how to do that before the due date since late assignments will not be
graded until the next grading period. Valid program format: a single file named pr2.c